In eukaryotes, multiprotein complexes termed TOR complex 1 (TORC1) and TOR complex 2 (TORC2) function as major regulators of cell growth, metabolism and ageing. The C-terminal domain of the Saccharomyces cerevisiae TORC2 component Avo1 is required for plasma-membrane localization of TORC2 and is essential for yeast viability. X-ray crystal structures of the C-terminal domain of Avo1 and of its human orthologue Sin1 have been determined. The structures show that the C-termini of Avo1 and Sin1 both have the pleckstrin homology (PH) domain fold. Comparison with known PH-domain structures suggests a putative binding site for phosphoinositides.